Dams inevitably result in species decline on reservoir islands

Hydropower development is booming, with controversial projects unfolding across the Americas, Africa, Asia and Europe.

Though often presented as a green renewable energy option, dams can cause a litany of negative impacts: disrupting the downstream flow of nutrients, interrupting aquatic migration routes and harming fisheries. They flood forests, destroy habitat and increase the release of greenhouse gases as vegetation decomposes. Dams also displace human communities — submerging homes and indigenous territories.

A new study adds another impact to the list, one that is widespread but has so far been overlooked by dam developers: “extinction debt” — the incremental but inexorable loss of species and diminishment of biodiversity over time on islands created by reservoirs.

Hydropower developers have long claimed reservoir islands as quality habitat and as viable conservation areas — both assertions are false, according to the new research.

A global evaluation of reservoir islands

The study, led by Isabel Jones at the UK’s Stirling University, collated biodiversity data from 100 studies of reservoir islands — with time since habitat isolation ranging from 1 to 92 years — at 15 dams in North, Central and South America, Europe, and Asia.

In more than 75 percent of cases studied, dams had an overall negative impact on reservoir island species, affecting factors such as species population density, ecological community composition, and species behavior.

Thousand Island Lake in China, the result of a dam built in the 1950s on the Xin’an River, was one of 15 dams worldwide included in a recent study that concluded that reservoir islands should not be counted as conservation areas by developers. Photo by Bryan Ong on Flickr, under a Creative Commons CC BY-NC-ND 2.0 license